The invention relates to a device for controlling an internal combustion engine driving a utility unit, with a speed control circuit for the internal combustion engine and with a load control circuit for the utility unit.
In particular when a load on the utility unit changes as a function of the engine speed, which speed also represents a controlled variable of the speed control circuit for the internal combustion engine, the two control circuits are coupled by the common controlled variable representing the engine speed. Under certain conditions, this coupling results in interactions which can lead to an unstable behavior of the system as a whole. In such known devices, in which the control circuits have only common information available via a particular reference variable or a controlled variable, no operating condition-defining variables are analyzed.
An internal combustion engine mechanically coupled to a hydraulic pump is known from EP 0 736 708 A1, wherein the displaced volume of the hydraulic pump is adjusted proportionally to the speed of the drive engine. This takes place via a mechanically coupled control valve. System-critical or dynamically relevant state constellations cannot be taken into account in this known device, and no control intervention in an electronic control circuit is possible.
It is an object of the present invention to provide a device with which, in an internal combustion engine/utility unit system, the control circuits for the speed of the internal combustion engine and the unit load can be decoupled according to particular requirements upon the occurrence of system-critical and dynamically relevant signal and state constellations.
The device according to the invention provides for a reduction in the system complexity and thus a better control of the dynamics of the system as a whole is achieved by virtue of the state-dependent task separation or decoupled control. Unstable system states can be avoided by specific intervention in particular in the load control circuit but if required in the speed control circuit as well. For example, the control on the utility unit side can be deactivated in during temporary engine output limitation, so that the internal combustion engine has the opportunity to build the necessary torque up again while loading remains unchanged. After this unsteady operating phase has ended, the control of the utility unit is enabled again.
Such interventions are preferably changes in controller parameters and/or activations, deactivations or restrictions of at least one of the control circuits. In this connection, the intervention means are designed above all and essentially for intervention in the load control circuit. However, interventions in the speed control circuit are also possible.
In a preferred application, the intervention means can be activated on temporary output limitations of the internal combustion engine. Then, preferably, an intervention in the load control circuit is performed.
The engine speed preferably serves as the reference variable and controlled variable for both control circuits.
In an advantageous embodiment, at least the input variables engine speed, maximum engine torque and actual engine torque, and preferably also the input variable ambient pressure, are applied to the means for detecting and evaluating the system state. From these variables, preferably at least two of the system states, that is, full output, temporarily restricted output and unrestricted output states are then detected and evaluated.
Comparison arrangements for comparing the maximum possible engine torque with the instantaneous full-load value and/or for comparing the maximum possible engine torque with the actual engine torque value preferably serve for evaluation. In this connection, an evaluating arrangement for the results of the comparison serves for detecting the different system states, depending on which the interventions in the control circuit(s) in turn take place.
Any simultaneous meeting of a number of decision conditions is excluded in an advantageous manner by a prioritization arrangement.
In a preferred application, the internal combustion engine is designed as a supercharged internal combustion engine, in particular as a diesel engine, and the utility unit can be a mechanical or hydromechanical gearing or a converter or a hydraulic pump.
The invention will become more readily apparent from the following description of a preferred embodiment thereof described below on the basis of the accompanying drawings.